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Genes involved in bacitracin resistance in Streptococcus mutans
Hiromasa Tsuda1, Yoshihisa Yamashita, Yukie Shibata
1Department of Preventive Dentistry, Kyushu University Faculty of Dental Science, Fukuoka 812-8582, Japan.
Antimicrobial Agents and Chemotherapy
|November 19, 2002
Summary
Streptococcus mutans resistance to bacitracin involves two genetic loci. Rhamnose-glucose polysaccharide (RGP) synthesis contributes to resistance, while mbr genes provide significant, independent modulation of bacitracin sensitivity.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Streptococcus mutans exhibits intrinsic resistance to the peptide antibiotic bacitracin.
- Understanding the genetic basis of this resistance is crucial for potential therapeutic strategies.
Purpose of the Study:
- To elucidate the molecular mechanisms underlying bacitracin resistance in Streptococcus mutans.
- To identify and characterize the specific genes and pathways involved in conferring resistance.
Main Methods:
- Cloning and sequencing of two Streptococcus mutans genetic loci associated with bacitracin resistance.
- Construction and phenotypic analysis of gene inactivation mutants for rgp and mbr genes.
- Comparative assessment of bacitracin sensitivity in wild-type and mutant strains.
Main Results:
- The rgp locus, encoding components for rhamnose-glucose polysaccharide (RGP) synthesis, was identified. Inactivation of RGP synthesis led to a fivefold increase in bacitracin sensitivity.
- A second locus containing mbr genes (mbrA-D) was identified. Mutants lacking functional mbr genes exhibited 100-120-fold higher sensitivity to bacitracin.
- Combined inactivation of RGP synthesis and mbr genes resulted in even greater bacitracin sensitivity.
Conclusions:
- Rhamnose-glucose polysaccharide (RGP) synthesis plays a role in Streptococcus mutans' resistance to bacitracin.
- The mbr genes independently modulate bacitracin resistance through a mechanism distinct from RGP synthesis.